Advanced Damping Materials for Marine Applications - ACS Publications

Chapter 21

Advanced Damping Materials for Marine Applications

Downloaded by UNIV MASSACHUSETTS AMHERST on September 4, 2013 | http://pubs.acs.org Publication Date: May 1, 1990 | doi: 10.1021/bk-1990-0424.ch021

Usman Sorathia, William Yeager, and Timothy Dapp David Taylor Research Center, Annapolis, MD 21402-5067

Viscoelastic IPNs have potential utility in many noise and vibration damping applications. Three groups of simultaneous polyurethane (4,4 diphenyl methane diisocyanate, polytetramethylene ether glycol, butanetanediol)/Epoxy (diglycidylether of bisphenol A, boron trichloride amine complex) IPNs were synthesized varying only the molecular weight of polyurethane component polyol. The polyols were selected at the molecular weights of 650, 1000, and 2000. These IPNs were characterized by density measurements, dynamic thermal mechanical analysis, and transmission electron microscopy. Results show an increase in glass transition temperature (Tg) for the polyurethane component as molecular weight of the polyol decreases, and a significant broadening of Tg at or around PU/EP composition of 70/30. This is true for all three groups studied. At this composition, storage modulus showed much less steep variations with temperature during the transition from glassy to rubbery state.

V i s c o e l a s t i c I n t e r p e n e t r a t i n g Polymer Networks (IPNs) have p o t e n t i a l u t i l i t y i n many noise and v i b r a t i o n damping a p p l i c a t i o n s . Interpenetrating Polymer Networks (IPN) are a new c l a s s of m a t e r i a l s c o n s i s t i n g o f m u l t i component c r o s s l i n k e d polymer systems. IPNs are d i s t i n guished from t h e i r parent polymer m a t e r i a l s by a general c h a r a c t e r i s t i c that c r o s s l i n k i n g occurs e x c l u s i v e l y i n , This chapter not subject to U.S. copyright Published 1990 American Chemical Society

In Sound and Vibration Damping with Polymers; Corsaro, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.


21. SORATHIA ET AL.

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383

but not between, the d i s t i n c t polymer systems (1). I n t i mate component mixing during c r o s s l i n k i n g r e s u l t s i n permanent p h y s i c a l entanglement of the polymer chains and g i v e s r i s e t o unique p h y s i c a l and dynamic p r o p e r t i e s u n a t t a i n a b l e i n s i n g l e component systems, g r a f t copolymers or compatible polymer blends (2). Of p a r t i c u l a r i n t e r e s t t o the Navy i s the enhanced n o i s e and v i b r a t i o n damping performance e x h i b i t e d by c e r t a i n IPN systems over wide temperature ranges. Even though the performance of any sound damping m a t e r i a l system i s u l t i m a t e l y determined by i t s a p p l i c a t i o n , r e l a t i v e performance e v a l u a t i o n and ranking f o r m a t e r i a l s of i n t e r e s t can be obtained from dynamic-mec h a n i c a l a n a l y s i s techniques designed t o provide v i s c o e l a s t i c ( v i b r a t i o n damping) property i n f o r m a t i o n . Spec i f i c a l l y , t h i s technique provides storage modulus, E* ( e l a s t i c response); l o s s modulus, E" (viscous response); and l o s s tangent, tan 6 ( E " / E ) . A l l polymer systems e x h i b i t a maximum value f o r tan 6, and hence maximum damping e f f i c i e n c y a t t h e i r g l a s s t r a n s i t i o n temperat u r e , Tg. Two component ( d i f f e r e n t Tg), p a r t i a l l y misc i b l e IPNs t y p i c a l l y show c h a r a c t e r i s t i c "inward" s h i f t s of l o s s tangent where the component peaks are b l u r r e d i n t o a c e n t r a l r e g i o n of r e l a t i v e l y constant tan S r e sponse. Chang, Thomas and S p e r l i n g (2) have subsequentl y shown t h a t the area under the l i n e a r l o s s modulus versus temperature curve obeys l i n e a r mixing r u l e s f o r c e r t a i n s e q u e n t i a l IPNs, e s s e n t i a l l y c o n f i r m i n g t h a t , i n general, IPNs d i s t r i b u t e the same amount of damping " e f f i c i e n c y " per u n i t volume of m a t e r i a l over a wider temperature range. An e a r l y attempt t o u t i l i z e the v i b r a t i o n absorbing e f f e c t of an IPN mixture was made by S p e r l i n g e t a l (4), who produced " S i l e n t Paint", of which one l a y e r was an IPN. Hourston et a l (5) i l l u s t r a t e d t y p i c a l IPN behavi o r i n a 1:1 weight r a t i o P o l y e t h y l a c r y l a t e / P o l y e t h y l m e t h a c r y l a t e l a t e x IPN. A continued need f o r s i m i l a r types of m a t e r i a l s has prompted i n v e s t i g a t i o n of a l l polymeric m a t e r i a l s known t o be e f f e c t i v e energy absorbers. f

EXPERIMENTAL In t h i s work, polyurethane (PU) and epoxy (EP) mixtures were s e l e c t e d f o r i n v e s t i g a t i o n because they are known t o form p a r t i a l l y m i s c i b l e IPNs with broad g l a s s t r a n s i t i o n temperatures. These were f i r s t prepared by F r i s c h et a l ( 6 ) u s i n g a simultaneous p o l y m e r i z a t i o n technique i n bulk. These m a t e r i a l s showed the e f f e c t s of c r o s s l i n k i n g only one polymer component (pseudo-IPN) and i n t e n t i o n a l g r a f t i n g between the component polymers. Klempner e t a l (2) a l s o studied PU/EP IPNs f o r v i b r a t i o n a t t e n u a t i o n . The polyurethanes i n t h i s work were c h a i n extended and c r o s s l i n k e d with a 4:1 e q u i v a l e n t r a t i o of b u t a n e d i o l (BD) and t r i m e t h y l o l propane (TMP).



384

SOUND AND VIBRATION DAMPING WITH POLYMERS

In our work, PU/EP SINs were prepared from a p o l y u rethane component c o n s i s t i n g of 4,4 diphenyl methane d i i s o c y a n a t e (MDI, Isonate 125M, Upjohn Chemicals) and polytetramethylene ether g l y c o l (Teracol, DuPont Chemic a l Co.) a t d i f f e r e n t molecular weights of 650, 1000, and 2000. Butanediol (BD) was the chain extender and t r i m e t h y l o l propane (TMP) the c r o s s l i n k i n g agent i n a BD:TMP equivalent r a t i o of 7:1. An isocyanate index of 1.1 was used f o r a l l formulations. No c a t a l y s t was used t o maximize the pot l i f e . The epoxy component c o n s i s t e d of d i g l y c i d y l ether of bisphenol A (DER 332, Dow Chemic a l ) cured with a boron t r i c h l o r i d e amine complex (DY 9577, Ciba-Geigy) as the l a t e n t c u r i n g agent at a r a t i o of 5 p a r t s per hundred (phr). A l l m a t e r i a l s were used as r e c e i v e d from the manufacturer except p o l y o l s which were heated at reduced pressures to remove d i s s o l v e d water. Tables I,II,and I I I summarize the IPNs produced i n Group 1 ( p o l y o l 650 Mw), Group 2 ( p o l y o l 1000 Mw), and Group 3 ( p o l y o l 2000 Mw). Simultaneous PU/EP IPNs were prepared by a c a s t i n g technique. The p o l y o l was heated t o 100-110°C a t reduced pressure f o r one hour. I t was cooled t o 60°C and the isocyanate and epoxy r e s i n were added. The preheated, premixed mixture of extender and c r o s s l i n k i n g agents f o r polyurethane and epoxy were then added and mixed t h o r oughly. The mixture was poured i n t o a preheated mold, allowed t o g e l , and cured f o r 16 hours at 110°C. Rods of approximately 3/16" diameter X 12" were a l s o produced f o r dynamic mechanical t e s t i n g . Very e a r l y i n t h i s phase of work, i t was recognized t h a t c u r i n g of epoxy r e s i n s with conventional c u r i n g agents, such as primary and secondary diamines, d i d not work w e l l . As soon as the component A ( c o n s i s t i n g of epoxy r e s i n , p o l y o l , isocyanates) was mixed with component B ( c o n s i s t i n g of c a t a l y s t , c u r i n g agent, and c r o s s l i n k i n g agent), amines reacted with isocyanates t o produce a non-castable s o l i d mass t h a t could not be e a s i l y processed. Limited success was achieved by c u r i n g epoxy r e s i n with l i q u i d anhydride (nadic methyl anhydride) but t h i s system produced some bubbles i n t o the c a s t samples. Best r e s u l t s were obtained when a c a t a l y t i c c u r i n g agent, such as boron t r i c h l o r i d e amine complex, DY 9577, was used. In t h i s case, the c u r i n g agents are not cor e a c t a n t s , but serve t o c a t a l y z e homopolymerization of the epoxy r e s i n . T h i s complex of Lewis a c i d r e q u i r e d c u r i n g a t elevated temperatures as i t has n e g l i g i b l e reactivity a t room temperature. These formulations produced s a t i s f a c t o r y c a s t a b l e mixtures that could be processed e a s i l y by pouring i n t o the mold or tube and c u r i n g i t i n the oven. Samples were produced r e l a t i v e l y f r e e of bubbles.


21. SORATHIA ET AL.

Damping Materials for Marine Applications 385

RESULTS AND DISCUSSIONS The pure components, as w e l l as IPNs produced a t v a r i o u s r a t i o s , were c h a r a c t e r i z e d by d e n s i t y measurements, dynamic thermal mechanical a n a l y s i s , and e l e c t r o n microscopy. R e s u l t s are presented and d i s c u s s e d below.


Table I . Group 1 IPNs -

PTMEG 650 (PU)

PU/EP RATIO

SPECIFIC GRAVITY

100/0 90/10 80/20 70/30 60/40 50/50 0/100

1.1239 1.1434 1.1508 1.1596 1.1561 1.1768 1.1966

Table I I . Group 2 IPNs -

PTMEG 1000 (PU)

PU/EP RATIO

SPECIFIC GRAVITY

100/0 90/10 70/30 50/50 0/100

1.0965 1.1156 1.1298 1.1510 1.1966

Table I I I . Group 3 IPNs - PTMEG 2000 (PU) PU/EP RATIO

SPECIFIC GRAVITY

100/0 84/16 72/28 56/44 0/100

1.0598 1.0824 1.0999 1.1262 1.1966



386


DENSITY. The s p e c i f i c g r a v i t y of a l l formulations was measured by a displacement method i n accordance with ASTM D792. The d e n s i t y composition data f o r Groups 1,2,and 3 are shown i n F i g u r e 1. S t r a i g h t l i n e s were drawn f o r each system based on a l i n e a r r u l e of mixtures . The d e n s i t y composition curves show i n c r e a s e d d e n s i t y over t h a t expected u s i n g the l i n e a r r u l e of mixtures f o r a l l IPN samples. IPN samples based on PTMEG 650 (Group 1) e x h i b i t e d the highest i n c r e a s e i n d e n s i t y where as samples based on PTMEG 2000 (Group 3) showed the l e a s t i n c r e a s e i n d e n s i t y . As d i s c u s s e d l a t e r , Group 3 m a t e r i a l s showed r a t h e r broad g l a s s t r a n s i t i o n temperatures . Observed IPN d e n s i t i e s , higher than those p r e d i c t e d by a l i n e a r r u l e of mixtures assumption, have been i n t e r p r e t e d t o i n d i c a t e the degree of molecular mixing (7) and hence the extent of system i n t e r p e n e t r a t i o n . Kim e t a l (8) have explained the increased d e n s i t y of IPNs q u a l i t a t i v e l y by means of chain entanglements a t the domain boundaries. DYNAMIC THERMAL MECHANICAL ANALYSIS. As mentioned p r e v i o u s l y , the purpose of t h i s study i s t o s y n t h e s i z e systems which produce broad g l a s s t r a n s i t i o n s . Using W i l l i a m , Landel, Ferry (WLF) frequency-time s u p e r p o s i t i o n i n g techniques, i t can be shown t h a t broad m a t e r i a l tan S values ( over a given temperature range ) t r a n s l a t e i n t o s i m i l a r tan 6 performance over a much wider frequency range. The usual accepted r e l a t i o n s h i p i s approximately one decade of frequency f o r every 5-8°C temperature increment. In an optimized IPN system, with e l e v a t e d tan 6 values over a f a i r l y wide temperature range (50°C), WLF a n a l y s i s would i n d i c a t e e f f e c t i v e sound damping performance over 6-10 decades of frequency. T h i s would be a s i g n i f i c a n t improvement over s t a t e o f - t h e - a r t damping m a t e r i a l s . Although the molecular b a s i s of damping i s not y e t completely understood, f e a t u r e s such as f l e x i b l e chains rubbing over s t i f f e r ones are thought t o be important. For o b t a i n i n g a broad g l a s s t r a n s i t i o n range, i t i s r e q u i r e d t h a t compositions be n e a r l y , but not q u i t e , misc i b l e and t h a t the domains of these phases be very small i n order t o e x h i b i t one very broad peak . Compositions t h a t are immiscible e x h i b i t two g l a s s t r a n s i t i o n s and two tan S-temperature peaks with r e l a t i v e l y l i t t l e damping i n the area between them. Compositions with a homogeneous amorphous phase e x h i b i t a s i n g l e g l a s s t r a n s i t i o n . A s i n g l e g l a s s t r a n s i t i o n y i e l d s good evidence of molecular mixing, provided t h a t the g l a s s t r a n s i t i o n s of the homopolymers are d i f f e r e n t and the g l a s s t r a n s i t i o n of the mixture i s intermediate between the two.


21. SORATHIA ET AL.


The dynamic mechanical property data f o r Groups 1,2,and 3 m a t e r i a l s were obtained from a Polymer Laborat o r y Model 983 Dynamic Mechanical Thermal A n a l y z e r (DMTA), and i n c l u d e l o g tan 6 ( l o s s f a c t o r ) , l o g E ( s t o r a g e modulus), and l o g E " ( l o s s modulus). Frequency was h e l d constant a t 10 Hz f o r a l l samples. The superposed r e s u l t s are shown f o r each group i n F i g u r e s 2-10. Samples produced i n a l l three groups e x h i b i t e d g l a s s t r a n s i t i o n peaks which were intermediate between the g l a s s t r a n s i t i o n temperature range o f polyurethane and epoxy a t low concentrations o f epoxy component. T h i s would i n d i c a t e enhanced i n t e r p e n e t r a t i o n with very l i t t l e o r no phase separation. Around PU/EP r a t i o of 70/30, broadening o f g l a s s t r a n s i t i o n i s observed, and phase s e p a r a t i o n does become evident as the c o n c e n t r a t i o n o f epoxy component i n creases. Of p a r t i c u l a r importance was the f a c t t h a t a broadening o f the g l a s s t r a n s i t i o n temperature r e g i o n i s a l s o accompanied by f l a t t e n i n g o f modulus curve. A l s o , broadening the g l a s s t r a n s i t i o n temperature r e g i o n f o r the IPN system r e s u l t s i n a lowering o f the maximum t a n S v a l u e s . T h i s i s compensated f o r by t h e broadening o f tan S curves t o introduce l o s s i n e s s i n IPN m a t e r i a l s i n the frequency bands not p r e v i o u s l y covered by t h e pure components.


1

ELECTRON MICROSCOPY. Transmission e l e c t r o n microscopy was done with a P h i l i p s 420 STEM on samples microtomed at -78°C with an RMC ultramicrotome. Samples were s t a i n e d by p l a c i n g the microtomed s e c t i o n s on e l e c t r o n microscopy g r i d s i n ruthenium t e t r a o x i d e vapor f o r 15 minutes. E l e c t r o n micrographs f o r the samples belonging t o Group 2 are shown i n Figures 11-15. The ruthenium t e t raoxide vapor, which was used t o s t a i n the samples, p r e f e r e n t i a l l y s t a i n s double bonds. Because o f the ext e n s i v e saturated hydrocarbon regions i n the p o l y u r e t h anes, they contain fewer double bonds than does epoxy. Therefore epoxy i s p r e f e r e n t i a l l y s t a i n e d by ruthenium t e t r a o x i d e , and i s b e l i e v e d t o account f o r the darker f e a t u r e s on the micrograph. The pure m a t e r i a l s showed no phase s e p a r a t i o n ( F i g ures 11 & 12). The 50/50 PU/EP sample, shown i n F i g u r e 13, has features o f two d i f f e r e n t s i z e s . There a r e e l o n gated features approximately 20 nm i n length and chain l i k e features approximately 5 nm wide. The dark epoxy regions are l a r g e r than i n the 70/30 PU/EP mixture shown i n Figure 14. For t h i s sample, chains o f polyurethane approximately 5 nm i n width appear t o permeate and s u r round the epoxy domains which are about 2 nm i n diamet e r . The 90/10 PU/EP mixture had a much more v a r i e d appearance than d i d the other two mixtures. Polyurethane


388


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SORATHIA ET AL.

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Figure 6. Composite l o g (E ) vs Temperature f o r Group 2 IPNs, PTMEG 1000(PU).



SORATHIA ET AL.

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21.

SORATHIA ETAL.


F i g u r e 11. E l e c t r o n Micrograph, 100% PU

F i g u r e 12. E l e c t r o n Micrograph, 100% EP



394


Figure 13. E l e c t r o n Micrograph, 50/50 PU/EP

Figure 14. E l e c t r o n Micrograph, 70/30 PU/EP



SORATHIA ET AL.

Figure

15.

Damping Materials for Marine Applications

Electron Micrograph,

90/10

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396


predominates, and the epoxy features are much more separ a t e d than i n the other two samples. F i v e nm p o l y u r e t h ane f e a t u r e s are a l s o evident f o r t h i s sample as shown i n F i g u r e 15.


CONCLUSIONS Simultaneous PU/EP IPNs were synthesized and c h a r a c t e r i z e d by d e n s i t y measurements, dynamic thermal mechanical a n a l y s i s , and t r a n s m i s s i o n e l e c t r o n microscopy. Higher m i s c i b i l i t y , increased d e n s i t y , and h i g h e r g l a s s t r a n s i t i o n temperature f o r Group 1 m a t e r i a l s was obtained using lower molecular weight p o l y o l (mw 650) and producing s h o r t e r polymer segment lengths. Dynamic thermal mechanical a n a l y s i s i n d i c a t e s s i g n i f i cant broadening o f g l a s s t r a n s i t i o n temperature a t o r around PU/EP composition o f 70/30. T h i s i s t r u e f o r a l l three groups s t u d i e d . At t h i s composition, storage modul u s showed much l e s s steep v a r i a t i o n s with temperature during the t r a n s i t i o n from g l a s s y t o rubbery s t a t e . ACKNOWLEDGMENTS The authors wish t o express t h e i r thanks t o Dr. B. Howe l l and Mr. H. Telegadas, both o f the David T a y l o r Research Center, f o r t h e i r t e c h n i c a l a s s i s t a n c e . Dr. B. Howell produced the e l e c t r o n micrographs. REFERENCES 1. Sperling, L . H. Interpenetrating Polymer Networks and Related Materials, Plenum Press, New York, 1981. 2. Klempner, D . ; Frisch, K. C . ; Xiao, X. H . ; Frisch, H. L. Two and Three Component Interpenetrating Polymer Networks, Polymer Engineering and Science, V o l . 25, No. 8, June 1985. 3. Chang,M.C.O.; Thomas, D . A . ; Sperling L . H . J. Applied Polymer Sc., 34, pp.409-422, (1987). 4. Sperling, L . H . ; Chin, T.W.; Giamlich, R.G; Thomas, D.A. Synthesis and Behavior of Prototype Silent Paint, Journal of Paint Technology, V o l . 46, No. 588, Jan. 1974. 5. Hourston, D . J . ; R. Satgurunathan; H. Varma, J. Appl. Polymer Sc., 31, 1955 (1986). 6. Frisch, H . L . ; Frisch, K . C . ; Klempner, D. Polym. Eng. S c i . , 14 (9), 646, 1974. 7. Frisch, H . L . ; Frisch, K . C . ; Klempner, D. Advances in Interpenetrating Polymer Networks, Pure & Appl. Chem., Vol.53, pp. 1557-1566, Printed in Great B r i t a i n . 8. Kim, S . C . ; Klempner, D . ; Frisch, K . C . ; Radigan, W.; Frisch, H . L . Macromolecules, 9, 258 (1976). RECEIVED January 24, 1990


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